COMPOSITES FOR BUOYS 1

[CRF59]

I have been working on new ocean buoy designs lately and have questions concerning the use of composites to replace metal frames. We use aluminum for many buoy hulls at present and for almost all of our superstructures. I am investigating the use of ionomer foam hulls (Gilman Softlite) which offers great potential. What I don't like is the continued use of aluminum for frames since I have to deal with long-term maintenance issues (corrosion, pitting, sandblasting, painting, etc). For a fleet of almost 300 buoys and growing, this is a big deal.

Are there any composites (fiberglass, carbon, etc) out there that can tolerate extended (multi-year) submersion in seawater without gel coatings or other surface finishing? We don't want high porosity either as this diminishes our reserve buoyancy.

 

[CompositeGeek]

Search internet under "marine composite applications" and you will find a huge number of hits for a variety of materials that stand up well in marine environments from a large number of sources.



Composites and Airplanes - what was I thinking?

There are gremlins in the autoclave!

 

[CRF59]

Howdy,

Well, I've tried most of those links and they're for the most part chest-thumping on the part of vendors. What I want are test results, evaluations, and examples of successful applications. Everyone is trying to protect their IP so it's tough to get meaningful information.

In a nutshell, I'm looking for materials to fabricate buoy frames and towers from that are lighter in weight, at least as strong, and hold up better in an ocean environment than 6000-series aluminum and steel. I know many fiberglass materials absorb water if not gell-coated, etc. That would marginalize my reserve buoyancy and present long-term reliability issues. So my needs are less about the advantages of composites than finding the right composite. I find that information harder to uncover.

 

[rnd2]

Epoxy-vinyl-ester resin composites are unaffected by long term exposure to seawater. If you want to get additional information/second opinions about that just enter search words hull blisters/blistering, swimming pool blisters, marine surveyor blister. For industrial applications where pretty doesn't matter, I am sure you will reach a conclusion that when using a resin such as epoxy vinyl ester, as well as some other completely water resistant resins such as phenolic, surface gelcoating is a waste of time and money. For a composite long term immersed in water, it is unavoidable for water to enter voids via various entry mechanisms such as micro-fissures, contraction micro-cracks in resin rich zones, capillary action along exposed glass fibers, and general osmosis, but long term, the resin remains unaffected by exposure to seawater. Long term meaning >20 years.
My company manufactures epoxy vinyl ester tubes using a centrifuge system developed in-house. Other processes to make structural shapes use pultrusion and filament winding processes. For complex shapes and flat sheets there are vacuum bagging and sheet moulding techniques. Even hand lay up is still used.
Start looking for manufacturers of structural materials that can demonstrate they can and are willing to manufacture structural composites from epoxy vinyl ester resin and glass fiber. If you are unsure about starting there, epoxy vinyl ester resin makers such as Dow Chemicals are a good place to start looking and I am sure they will put you in touch with the right fabricators.
One last thing, given that yours is a high UV exposure application, UV protection is a must to prevent long term material degradation.

 

[microthene]

You may want to use a compression molded composite (Sheet moldin compound). There is little to no porosity when manufactured. SMC can be made from fiberglass or carbon fiber, and the resin can be vinylester, polyester, epoxy, and other hybrids. SMC can be molded into channels or angles.

Pultrusion composites are another option.
Higher strength in machine direction, but more susceptible to porosity, but can be manufactured into more complex shapes, like I beams.

Most compression molders and pultruders have resin suppliers that can supply the best corrosion resistant and uv resistant resins.

http://www.strongwell.com

http://www.glastic.com

http://www.polyplycomposites.com

 

[Tofflemire]

Hi CFR59,

You can powder coat you aluminum and at a reasonable cost. Stay with aluminum, if you move to something new you will be finding all kinds of new problems.

Tofflemire

 

[Higgler]

Check out Nida-core in Florida.

http://www.nida-core.com/about_us.asp

They make boats. I inquired with them about antenna structures for use on outdoors antenna ranges. They use a wet-layup for their honeycomb core and skins. I believe that means that epoxy resin is everywhere (honeycomb is immersed in resin) so that the sea water can't propagate a crack if something gets perforated. 4x8 foot sheet for $800, 3/4 inch thick, less then one lb per square foot weight and pretty darn strong.
Edges of the material must be closed off and UV protected.

A boat builder sounds like a good choice.

kch

 

[PanelGuy]

WAAAY back in the day, Eric Miller Associates published a survey of Marine Composites for the Navy. It is still applicable today. Searching the above should find it.

Nida-Core produces cores and panels are are not good for much else.

It really depends on what your goals are. Exturded FRP pieces from Strongwell or others can give you the benefits of not really changing the design alot...buoys will still look like extruded tubes. Assembly will be different. You should be able to create fully bonded structures with no rivets, welding etc.

As well, You could do compression molding to create your sides and fasten top and bottom. Wet lay-up has become a good way to proto, but not consistent in the long run.

Companies like Mad River and We-No-Nah Canoe frequently are interested in stretch projects, where someone like Sea-Ray or Bayliner probably are not. Unfortunately they are not typically strong on design and analysis.

A good stabilized Epoxy or Vinylester molded with fiberglass and some protective veiling should be more than adequate. If you need some analysis work you may have to look around.

If you decide that flat panel machined to shape is a good way to go, let me know. We specialize in nontraditional laminated structures.

Good Luck.

 

[Higgler]

Panelguy,
have you built any panels for use in antennas? That was my reason for Nida-Core contacts. My needs are for outdoor or shipboard applications. I'm always looking for a source of lightweight honeycomb panels that can survive outdoors. Seems like delamination and UV damage are troublesome.

kch

PS: Sorry to diverge, but the buoy needs and my antenna needs are somewhat similar.

 

[PanelGuy]

kch -

We have. Mostly we tailor to customer needs. Look me up and I can get you a kit or trade info.

DGJ

Chief Engineer
Bellcomb.com